1. Field of the Invention
This invention relates generally to wiring aids for electricians. More particularly, this invention relates to an electrician's wiring aid to assist the electrician in the wiring of a three-phase switchboard or panelboard.
2. Description of the Background Art
Presently, switchboards and panelboards provide for the distribution of large blocks of power throughout a building. Switchboards, also commonly referred to as switch gear, are typically freestanding assemblies of switches, fuses and/or circuit breakers which provide switching and feeder protection to a number of feeder circuits connected to a main source, such as incoming electrical power from a power company. Panelboards serve basically the same function as switchboards except on a smaller scale. Namely, panelboards accept a relatively large block of electrical power via a feeder from the switchboard and distributes the power in smaller blocks for final distribution to branch circuits containing the electrical utilization apparatuses and devices such as lighting, motors and appliances. Like switchboards, panelboards comprise main buses to which are connected circuit protective devices (breakers or fuses) which feed the smaller branch circuits.
Typical panelboards comprise main buses which are mounted on an insulating board contained within an enclosing cabinet. Panelboards also include a neutral (ground) bus bar and a grounding bus bar. The conductors of a feeder are electrically connected to the respective bus bars and are typically required to be protected by a main circuit breaker. Each branch circuit is then electrically connected to the respective bus bars by means of a branch circuit breaker. More specifically, a three-phase panelboard typically includes three bus bars (one for each phase), a neutral or ground bus bar, and a grounding bus bar. The mechanical arrangement of the bus bars within the enclosure allows single, double and triple pole circuit breakers to be connected to the bus bars for supplying phase-to-neutral, phase-to-phase and three-phase electrical power to the branch circuit. Furthermore, the mechanical construction of the bus bars forces the circuit breakers to be connected thereto in a staggered configuration to enhance the equalization of the load on each phase.
Present electrical practice dictates certain color schemes for three-phase circuits. In the United States, such practice dictates that phases A, B and C are color coded black, red and blue, respectively, for 120/208 volt three-phase circuits; and, phase A, B and C are color coded brown, orange and yellow, respectively, for 277/480 volt and 240 volt center-tapped delta-connected three-phase circuits. For all voltage circuits, the ground conductor is color coded white and the grounding conductor is color coded green or comprises a bare, non-insulated conductor. Similar color conventions are in practice throughout the entire world; for example, the color scheme in practice in Canada is the same as that of the United States except that the colors for phase A and phase B of the circuits are reversed.
The need for a uniform color scheme is particularly useful when the feeder circuit comprises a four wire 240 volt centered-tapped delta-connected three-phase system in which the middle phase or leg (phase B) actually comprises a higher voltage to ground than the other two phases (phases A and C). Specifically, in a center-tapped 240 volt delta-connected three-phase system, the voltage of phases A and C to ground comprises 120 volts and the voltage between phases is 240 volts, but the voltage of phase B to ground is 208 volts. Hence, it is imperative to use the color scheme as it distinguishes the high phase or leg (phase B) at 208 volts from the 120 phase-to-neutral volts of the other phases (phase A and C). Without a color scheme, the electrician may inadvertently connect a 120 volt lighting or other load to the 208 volt high leg (phase B) of the system thereby imparting damage to the load or creating a safety hazard from an excessive voltage.
In view of the foregoing, the electrician must usually write down the color scheme outlined above on a scrap piece of paper prior to wiring a panelboard so that the electrician may refer to the color scheme during the wiring of the panelboard. Conformance with the color scheme is therefore assured. Hence, the electrician's work may be interrupted several times throughout a typical work day simply to assure conformance to the accepted color scheme.
Therefore, it is an object of this invention to provide an apparatus which overcomes the aforementioned inadequacies of the prior art devices and provides an improvement which is a significant contribution to the advancement of the electrical wiring art.
Another object of this invention is to provide means to increase the productivity of safely wiring a panelboard in conformance with a particular color scheme by eliminating the need of manually writing down the color scheme during the wiring of each panelboard.
Another object of this invention is to provide means for quickly and conveniently indicating to an electrician the color scheme for wiring three-phase panelboards, said means being incorporated in an existing tool commonly used by electricians.
Another object of this invention is to incorporate conventional color schemes for electrical wiring of panelboards with conventional rulers and other measuring devices commonly used by electricians.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure contained herein and in the above identified patents, the disclosure of which is hereby incorporated by reference herein. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.